Snyder, A. C., Kuipers, H., Cheng, B., Servais, R., & Fransen, E. (1995). Overtraining following intensified training with normal muscle glycogen. Medicine and Science in Sports and Exercise, 27, 1063-1070.

Low muscle glycogen levels can impair exercise performance at intensities primarily between 65 and 85% of VO2max, the exercise intensity at which most endurance athletes train. This study assessed whether the consumption of adequate amounts of CHO to maintain glycogen levels would protect athletes (trained cyclists; N = 8) from entering an overtained state.

Since no single physiological symptom or set of symptoms has been found to be associated with overtraining (p. 1065), five of the most observed symptoms were measured. If a subject displayed three of these five, it was inferred that an overtrained state had been achieved. The five symptoms were: a) decreased maximal workload, b) reduced HRmax, c) reduced resting plasma cortisol levels, d) reduced HLamax to RPE ratio, and e) an increased number of affirmative responses to a daily questionnaire about exercise stress symptoms.

Fourteen self-report questions assessed if Ss were: more quickly fatigued, not completely recovered, irritated more, less motivated, unable to complete the total training program, and were enjoying the sport less. Also evaluated were: performance decline, stiffness or pain in the muscles, problems with falling asleep, and diminution in appetite.

The supplementation of 160 g of CHO during all phases of training maintained consistent glycogen levels even when Ss indicated signs of overtraining. Ss had normal resting muscle glycogen levels but still became overtrained. Some mechanism other than resting muscle glycogen levels must be responsible for the occurrence of overtraining.

HRmax for exercise was significantly lower. A possible mechanism for this symptom could be a decreased maximal sympathetic drive. The reduction was also associated with reduced oxygen uptake. At low work levels, stroke volume was able to compensate for the lower HR and maintain oxygen uptake.

The psychological well-being of the Ss decreased during the period of heavy training. The question content with the largest increases in response embraced the following: a) more quickly fatigued, b) stiff and sore muscles, c) incomplete recovery, and d) greater difficulty in completing the training program. Six days of recovery was insufficient to promote full recovery of the self-report factors.

RPE did not differentiate similar workloads across the different training periods and was therefore, not sensitive to overtraining.

Implication. Overtrained states occurred despite maintaining consistent levels of muscle glycogen. Other factors, varying according to the individual, were associated with overtraining. Psychological reports of well-being were the most consistent indicators of overtraining.

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